Honda’s secret F1 hybrid

The first F1 team to develop a hybrid car was McLaren, with a still largely secret KERS in 1998. The technology was quickly banned and was only permitted to return in 2009. History shows that the re-introduction of hybrid systems was not a huge success, most teams struggled to get the technology to work properly and only a few teams actually raced with it.

However one team that would have done so, if they had ever built their 2009 car was Honda. The stillborn RA109 was from the outset designed to be fitted with a highly innovative battery-electric hybrid system. This system was first used in straight line testing in April 2008, and in May of that year, at Silverstone, Honda was the first F1 team to test a hybrid system on a full track since McLaren a decade earlier.

The 2009 regulations stipulated that the KERS drive be limited to the rear wheels, that output should be no more than 60 kW, and that the amount of energy used per lap be no more than 400 kJ. Honda had been conducting R&D in this area since the summer of 2007, and had developed a high speed, high output, direct oil-cooled motor, a water-cooled power control unit (PCU) which integrated a motor drive inverter unit and voltage control system, as well as a high power density lithium ion battery, all based on being small and lightweight enough for Formula One.

Because the overall system performance were stipulated by the regulations, Honda’s development focused on making the equipment as small and lightweight as possible. Development began in earnest in the summer of 2007, and in just nine months, track tests were conducted using the prototype vehicle RA1082 (a vehicle built to check the system functionality). The technology then went into the RA1089 (race prototype) and then it was planned to be installed in the RA109K (racing vehicle) in 2009. The RA109K tub was indeed built and crash tested with the system at least partially installed.The Honda RA109K being crash tested at Cranfield, it is thought that this chassis did not go to Brawn GP

Setting targets
Honda set some targets for the system, the weight must be no more than 30 kg (i.e., no more than 60% of the vehicle ballast weight of the 2006 vehicle), it must be able to be used for at least 5 continuous seconds at output of 60 kW (i.e., the output and assist time enabling the vehicle to overtake others).

When setting targets for performance, weight, center of gravity and the like for the various functional components, these parameters were investigated but the Honda engineers from many angles, including race strategy and the use of vehicle dynamics simulation, but some major concept related issues were encountered when doing these investigations.

One was whether the race strategy should emphasise overtaking or lap time. “We compared single assist, which uses the 400 kJ all at once, or multi assist, which splits the maximum 400 kJ to use it on multiple instances; simulations showed that compared to single assist, a multi-assist system that settled the energy budget at each corner could reduce lap times by about 0.1 seconds” Honda internal documents reveal.

Honda found that a multi-assist system allows smaller energy storage volume, so installation of a super capacitor with low energy capacity but great power density was considered. This would have a lesser impact on the chassis. “One cannot win a race unless one gets out ahead of other cars. For example, if assist is begun at 180 km/h, where the tyre grip exceeds the drive torque (i.e., the tyre is not skidding), assuming that the output of 60 kW will be used for 6.666 seconds (an energy equivalent of 400 kJ), vehicle speed can go 15 km/h faster than without assist, which in distance terms is a difference of 20 metres” The Honda documents continue. “Even supposing that it were not possible to use assist for 6.666 seconds because of the course layout or other reasons, this would be a distance gain of 5 m (one car length) in 2.78 seconds and 10 m (two car lengths) in 4.22 seconds over another vehicle, which allows overtaking, so single assist, in this case, is more effective in terms of race strategy.”

There was still not a clear agreement though on how to use the KERS in actual races, but after several discussions between Honda R&D engineers and Honda Racing F1 Team engineers, the concept of emphasizing overtaking was ultimately decided upon.

Part 1: Introduction
Part 2: Honda RA1082: Developing a hybrid system for use on a F1 car
Part 3: Honda RA1089: Finalising the hybrid system
Part 4: Honda RA109K: The final system examined
Part 5: The aftermath: What happened to Honda’s KERS?

Sam Collins has worked for Racecar Engineering for more than a decade. His passion for racing began during his work experience in the loom shop of Williams F1 aged 16 and he has been involved in the sport ever since. Sam attended Oxford Brookes University to study Automotive Engineering and has written for many publications since, including Motorsport News and Autosport. He is Associate Editor of Racecar Engineering

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